[commit: ghc] master: Fix typecheck of default associated type decls (cb24e68)
git at git.haskell.org
git at git.haskell.org
Mon Jan 18 10:43:27 UTC 2016
Repository : ssh://git@git.haskell.org/ghc
On branch : master
Link : http://ghc.haskell.org/trac/ghc/changeset/cb24e684759f3d181a104cde76f0f95da896a7ef/ghc
>---------------------------------------------------------------
commit cb24e684759f3d181a104cde76f0f95da896a7ef
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date: Mon Jan 18 10:43:47 2016 +0000
Fix typecheck of default associated type decls
This bug was thrown up by Trac #11361, but I found that the
problem was deeper: GHC was allowing
class C a where
type F (a :: k) :: *
type F (x :: *) = x -- Not right!
(Which is now indexed-types/should_compile/T11361a.)
Anyway the fix is relatively simple; use tcMatchTys in
tcDefaultAssocDecl.
Merge to 8.0 branch.
>---------------------------------------------------------------
cb24e684759f3d181a104cde76f0f95da896a7ef
compiler/typecheck/TcTyClsDecls.hs | 67 +++++++++++++++-------
.../should_compile/T11361.hs} | 5 +-
.../tests/indexed-types/should_compile/T11361a.hs | 7 +++
.../indexed-types/should_compile/T11361a.stderr | 5 ++
testsuite/tests/indexed-types/should_compile/all.T | 2 +
5 files changed, 65 insertions(+), 21 deletions(-)
diff --git a/compiler/typecheck/TcTyClsDecls.hs b/compiler/typecheck/TcTyClsDecls.hs
index e622c15..f6a5c9f 100644
--- a/compiler/typecheck/TcTyClsDecls.hs
+++ b/compiler/typecheck/TcTyClsDecls.hs
@@ -971,42 +971,64 @@ tcDefaultAssocDecl _ (d1:_:_)
tcDefaultAssocDecl fam_tc [L loc (TyFamEqn { tfe_tycon = L _ tc_name
, tfe_pats = hs_tvs
, tfe_rhs = rhs })]
- = setSrcSpan loc $
+ | HsQTvs { hsq_implicit = imp_vars, hsq_explicit = exp_vars } <- hs_tvs
+ = -- See Note [Type-checking default assoc decls]
+ setSrcSpan loc $
tcAddFamInstCtxt (ptext (sLit "default type instance")) tc_name $
do { traceTc "tcDefaultAssocDecl" (ppr tc_name)
- ; let shape@(fam_name, fam_pat_arity, _) = famTyConShape fam_tc
- fam_tc_tvs = tyConTyVars fam_tc
+ ; let shape@(fam_tc_name, fam_arity, _) = famTyConShape fam_tc
-- Kind of family check
- ; checkTc (isTypeFamilyTyCon fam_tc) (wrongKindOfFamily fam_tc)
+ ; ASSERT( fam_tc_name == tc_name )
+ checkTc (isTypeFamilyTyCon fam_tc) (wrongKindOfFamily fam_tc)
-- Arity check
- ; ASSERT( fam_name == tc_name )
- checkTc (length (hsQTvExplicit hs_tvs) == fam_pat_arity)
- (wrongNumberOfParmsErr fam_pat_arity)
+ ; checkTc (length exp_vars == fam_arity)
+ (wrongNumberOfParmsErr fam_arity)
-- Typecheck RHS
- -- Oddly, we don't pass in any enclosing class info, and we treat
- -- this as a top-level type instance. Type family defaults are renamed
- -- outside the scope of their enclosing class and so the ClsInfo would
- -- be of no use.
- ; let HsQTvs { hsq_implicit = imp_vars, hsq_explicit = exp_vars } = hs_tvs
- pats = HsIB { hsib_vars = imp_vars ++ map hsLTyVarName exp_vars
+ ; let pats = HsIB { hsib_vars = imp_vars ++ map hsLTyVarName exp_vars
, hsib_body = map hsLTyVarBndrToType exp_vars }
-- NB: Use tcFamTyPats, not tcTyClTyVars. The latter expects to get
-- the LHsQTyVars used for declaring a tycon, but the names here
-- are different.
- ; (ktvs, rhs_ty)
+ ; (pats', rhs_ty)
<- tcFamTyPats shape Nothing pats
- (discardResult . tcCheckLHsType rhs) $ \ktvs _ rhs_kind ->
+ (discardResult . tcCheckLHsType rhs) $ \_ pats' rhs_kind ->
do { rhs_ty <- solveEqualities $
tcCheckLHsType rhs rhs_kind
- ; return (ktvs, rhs_ty) }
-
+ ; return (pats', rhs_ty) }
+ -- pats' is fully zonked already
; rhs_ty <- zonkTcTypeToType emptyZonkEnv rhs_ty
- ; let subst = zipTopTCvSubst ktvs (mkTyVarTys fam_tc_tvs)
- ; return ( Just (substTy subst rhs_ty, loc) ) }
- -- We check for well-formedness and validity later, in checkValidClass
+
+ -- See Note [Type-checking default assoc decls]
+ ; case tcMatchTys pats' (mkTyVarTys (tyConTyVars fam_tc)) of
+ Just subst -> return ( Just (substTy subst rhs_ty, loc) )
+ Nothing -> failWithTc (defaultAssocKindErr fam_tc)
+ -- We check for well-formedness and validity later,
+ -- in checkValidClass
+ }
+
+{- Note [Type-checking default assoc decls]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this default declaration for an associated type
+
+ class C a where
+ type F (a :: k) b :: *
+ type F x y = Proxy x -> y
+
+Note that the class variable 'a' doesn't scope over the default assoc
+decl (rather oddly I think), and (less oddly) neither does the second
+argument 'b' of the associated type 'F', or the kind variable 'k'.
+Instead, the default decl is treated more like a top-level type
+instance.
+
+However we store the default rhs (Proxy x -> y) in F's TyCon, using
+F's own type variables, so we need to convert it to (Proxy a -> b).
+We do this by calling tcMatchTys to match them up. This also ensures
+that x's kind matches a's and similarly for y and b. The error
+message isnt' great, mind you. (Trac #11361 was caused by not doing a
+proper tcMatchTys here.) -}
-------------------------
kcTyFamInstEqn :: FamTyConShape -> LTyFamInstEqn Name -> TcM ()
@@ -2544,6 +2566,11 @@ wrongNumberOfParmsErr max_args
= ptext (sLit "Number of parameters must match family declaration; expected")
<+> ppr max_args
+defaultAssocKindErr :: TyCon -> SDoc
+defaultAssocKindErr fam_tc
+ = ptext (sLit "Kind mis-match on LHS of default declaration for")
+ <+> quotes (ppr fam_tc)
+
wrongTyFamName :: Name -> Name -> SDoc
wrongTyFamName fam_tc_name eqn_tc_name
= hang (ptext (sLit "Mismatched type name in type family instance."))
diff --git a/testsuite/tests/typecheck/should_compile/tc253.hs b/testsuite/tests/indexed-types/should_compile/T11361.hs
similarity index 83%
copy from testsuite/tests/typecheck/should_compile/tc253.hs
copy to testsuite/tests/indexed-types/should_compile/T11361.hs
index 2fd528b..61b412a 100644
--- a/testsuite/tests/typecheck/should_compile/tc253.hs
+++ b/testsuite/tests/indexed-types/should_compile/T11361.hs
@@ -1,7 +1,10 @@
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
-- this is needed because |FamHelper a x| /< |Fam a x|
-module ShouldCompile where
+{-# OPTIONS_GHC -dinitial-unique=16777000 -dunique-increment=-1 #-}
+ -- This is what made GHC crash before
+
+module T11361 where
class Cls a where
type Fam a b :: *
diff --git a/testsuite/tests/indexed-types/should_compile/T11361a.hs b/testsuite/tests/indexed-types/should_compile/T11361a.hs
new file mode 100644
index 0000000..66ab056
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T11361a.hs
@@ -0,0 +1,7 @@
+{-# LANGUAGE TypeFamilies, PolyKinds #-}
+
+module T11361a where
+
+class C a where
+ type F (a :: k) :: *
+ type F (x :: *) = x -- Not right!
diff --git a/testsuite/tests/indexed-types/should_compile/T11361a.stderr b/testsuite/tests/indexed-types/should_compile/T11361a.stderr
new file mode 100644
index 0000000..f7052ae
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T11361a.stderr
@@ -0,0 +1,5 @@
+
+T11361a.hs:7:3: error:
+ • Kind mis-match on LHS of default declaration for ‘F’
+ • In the default type instance declaration for ‘F’
+ In the class declaration for ‘C’
diff --git a/testsuite/tests/indexed-types/should_compile/all.T b/testsuite/tests/indexed-types/should_compile/all.T
index fe2688e..28ea8bd 100644
--- a/testsuite/tests/indexed-types/should_compile/all.T
+++ b/testsuite/tests/indexed-types/should_compile/all.T
@@ -271,3 +271,5 @@ test('T10318', normal, compile, [''])
test('UnusedTyVarWarnings', normal, compile, ['-W'])
test('UnusedTyVarWarningsNamedWCs', normal, compile, ['-W'])
test('T11408', normal, compile, [''])
+test('T11361', normal, compile, [''])
+test('T11361a', normal, compile_fail, [''])
More information about the ghc-commits
mailing list